RCB 9D-9 Model "4GC"


	ROCHESTER CARBURETORS Bulletin 9D-9 January 1952
	Page 4 ROCHESTER PRODUCTS, DIVISION OF GENERAL MOTORS, ROCHESTER, NEW YORK

	PERFORMANCE FEATURES

	The float bowls in the Model 4GC Carburetor completely encompass the main bores of the carburetor. This, plus the fact that a direct passage connects the main discharge nozzle wells and idle tube wells, provides for smooth operation regardless of the angle of tilt the car may assume. Another basic feature of all Rochester Carburetors also incorporated in the Model 4GC is the fixed type main metering jets. No wear takes place at the jet orifice. This carburetor model employs the use of a vacuum operated power system. In (his way proper power mixtures are readily available upon a drop in manifold vacuum, regardless of the degree of throttle opening. It is not necessary therefore, to open the throttle completely to enrich the mixture sufficiently for power operation. As in previous units, the Model 4GC Carburetor employs the use of a vented type pump plunger. By	means of a vent valve ball, within the plunger head itself, fuel vapors are allowed to pass from the pump well to the float bowl under constant throttle conditions. This insures that the pump well will be primed with solid fuel at ail times thereby being readily available for rapid acceleration. This pump system, as in the Model BB. is also vented to the bore of the carburetor air horn. This is done to prevent pump pullover or fuel being discharged from the pump jets during high speed operation. The chief feature, completely new to Rochester Carburetor design, is the secondary or fuel inlet side of the carburetor. This secondary side incorporates only three of the six basic systems of carburetion, those being Idle, Wide Open, and Float. The secondary throttle valves are controlled, through a series of linkages, by the primary or pump side throttle opening. The secondary side, by increasing air flow at high speeds, proportionately increases the engine's breathing capacity.

	SERVICE FEATURES

	The Model 4GC Carburetor, in keeping with all other Rochester designed carburetors, has been kept basically simple for case of service. 'A major portion of the calibrated metering parts is contained in the Venturi clusters, located in the float bowl and may be readily serviced by removing the Air Horn Assembly. The idle tubes and main discharge nozzles, being pressed into the Venturi clusters, need not be serviced separately.	The power restrictions and pump jets are also pressed in at the factory, thereby making individual replacement unnecessary. After the idling RPM has been set, no further ad-justment of the idle, part throttle, power or targeting of the pump jets is necessary. All field adjustments have been kept as simple as possible. For case in servicing this unit, the special tools, gauges, and field adjustments required have been kept to a minimum.